Balloon catheter

ABSTRACT

A balloon-tip catheter having a balloon formed from a polymeric material in the vicinity of the tip of a catheter, wherein the polymeric material forming the balloon comprises a polyolefin obtained by polymerization using a metallocene catalyst.

DESCRIPTION

1. Technical Field

The present invention relates to a balloon-tip catheter, andparticularly to a balloon-tip catheter having a balloon high instrength, excellent in flexibility, processability, shapeability,retention of shape, stability and fusion-bonding ability to a catheter.The balloon-tip catheter according to the present invention isparticularly suitable for use as a balloon-tip catheter for dilation fordilating a living organ or coeloma such as a vessel.

2. Background Art

A balloon-tip catheter is a tube provided with a balloon on its tip, andthe balloon may be inflated or deflated without drawing out the catheterafter insertion thereof. When the balloon-tip catheter is inserted intoa vessel to inflate the balloon, the inflated balloon is propelled byblood, so that the catheter is easily passed through the vessel. Avessel, through which the blood freely flows when the balloon isdeflated, may also be occluded by inflating the balloon.

Balloon-tip catheters are used in, for example, {circle around (1)}arterial embolization and thrombectomy, {circle around (2)} venousthrombectomy, {circle around (3)} dilation of a constricted artery,{circle around (4)} vascular embolization and vascular occlusion,{circle around (5)} removal of foreign matter in a vessel, etc., and areclassified into, for example, balloon-tip catheters for arterialthrombectomy, balloon-tip catheters for occlusion, balloon-tip cathetersfor vasodilation, etc. according to the respective uses and applicationsites thereof.

In recent years, medical techniques have trended toward low invasivetreatment against the human body. Among the balloon-tip catheters, anapplication range of the balloon-tip catheters for dilation for dilatingliving organs or coelomae has expanded in keeping with that. In general,the balloon-tip catheters for dilation have a structure that a balloon 2is arranged in the vicinity of the tip of a catheter 1 as illustrated inFIG. 1. The balloon 2 may be inflated by introducing a gas underpressure into the balloon 2 through an opening provided in the catheter1 or deflated by drawing the gas out of the balloon 2. The catheter 1 isgenerally equipped with various parts such as a side arm adapter 3 andan adapter 4.

In order to dilate a constricted artery, the outside of the body isfirst connected to an artery to be dilated by means of a vesselpuncturing device called a sheath introducer under local anesthesia, asheath serving as a passageway of a catheter is inserted into theartery, and a fine catheter is put in the artery through the sheath. Apressure-resistant balloon-tip catheter for dilation is then insertedinto the constricted part, and the balloon is inflated, thereby pressingthe hypertrophic tunica intima causing atheromatous degeneration againstthe tunica externa to dilate the lumen. This method is calledpercutaneous transluminal artery angioplasty and yields satisfactoryresults. The method is applied to, for example, a coronary artery, arenal artery, an external iliac artery, a femoral artery, etc. Thistreating method can greatly relieve patient's stress and also has aneconomical advantage. Accordingly, the constriction of a coronary arteryor the like is often treated by a vasodilative operation making use of aballoon-tip catheter for vasodilation in place of a coronary arterybypass operation or the like previously performed.

The application range of the balloon-tip catheters for dilation isexpanded making good use of their merits. Correspondingly, theballoon-tip catheters for dilation are also required to have highproperties. The balloon-tip catheters for dilation are required, forexample, {circle around (1)} to be able to treat the constriction of aperipheral coronary artery, {circle around (2)} to easily insert into acurved vessel, {circle around (3)} to have a strong dilation pressure,and to {circle around (4)} safely dilate a vessel.

More specifically, (1) it is required to be able to treat theconstriction of a more peripheral coronary artery than before using aballoon-tip catheter for vasodilation. In order to meet thisrequirement, formation of a balloon of low profile (reduction in theprojected area of the balloon in a longitudinal direction) is required.Therefore, a balloon of thinner wall and higher strength than before isrequired. (2) Cases of an intravascular operation, in which aballoon-tip catheter for dilation is inserted into a curved vessel,increase. In order to insert the catheter into the curved vessel withease, the balloon is required to be flexible and have trackability. (3)A stent is often left in a coeloma for support during anastomosis orafter the anastomosis, or ensuring the communication of the coeloma easyto constrict. In keeping with that, the balloon is required to have astronger dilation pressure. (4) As the intravascular operation isfrequently performed, it is required to be able to safely dilate avessel using a balloon-tip catheter for dilation. In order to meet thisrequirement, the balloon is required to have a compliance (i.e., rate ofchange in the diameter of the balloon inflated to the dilation pressureof the balloon) within a proper range and high breaking strength.

Polyethylene resins have heretofore been principally used as materialsof the balloon-tip catheters for dilation because they are comparativelygood in processability and balance among their properties. However, thepolyethylene resins heretofore used have involved a problem that theycannot fully meet the requirements as the requirement level against theproperties of the balloon-tip catheters for dilation is heightened. Theconventional balloon made of low density polyethylene (LDPE) isinsufficient in both strength and flexibility. Even when a linear lowdensity polyethylene (LLDPE) is used in place of LDPE, its improvingeffect on strength is a little, and only a balloon poor in flexibilitycan be obtained. Even when a balloon made of a polyethylene resin iscrosslinked by electron beam crosslinking, water crosslinking or thelike, any balloon excellent in balance among strength, flexibility,compliance upon inflation of the balloon, etc. cannot be obtained.

The balloon-tip catheter for dilation is shaped into a fixed form that aballoon is wound around a catheter in order to facilitate its insertioninto and extraction from a coeloma such as a vessel, and the fixed formis often retained while the balloon is deflated under reduced pressure.However, the balloon made of the conventional polyethylene resin hasbeen insufficient in shapeability and retention of shape. Balloonsmaking use of a polyamide resin or polyester resin have also been known.However, it is difficult to obtain a balloon excellent in balancebetween strength and compliance.

As described above, various resin materials have heretofore beeninvestigated as materials for forming a balloon of a balloon-tipcatheter for dilation. However, there has not been yet obtained anymaterial which can meet the above-described properties highly required.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a balloon-tipcatheter having a balloon which is high in strength, excellent inflexibility, easy to shape the balloon when it is folded, good insetting ability, has a compliance within a proper range when it isinflated, and moreover is excellent in processability, retention ofshape and fusion-bonding ability to a catheter.

The present inventors have carried out an extensive investigation with aview toward overcoming the above-described problems involved in theprior art. As a result, it has been found that a polyolefin obtained bypolymerization using a metallocene catalyst is used, thereby obtaining aballoon-tip catheter having good various properties. It has also beenfound that when an ethylene-α-olefin copolymer having specific physicalproperties is selectively used as the polyolefin, a balloon-tipcatheter, which can fully satisfied such highly required properties asdescribed above and is suitable for use as a balloon-tip catheter fordilation in particular, can be provided.

Recently, various kinds of polyethylene resins obtained by using ametallocene catalyst have come to be provided. Since the active site ofthe metallocene catalyst is single, a polyolefin having even molecularweight and composition and high impact strength and transparency can beprovided. In the case of, for example, an ethylene-α-olefin copolymer,polyethylene resins greatly different in density and performance can beprovided by using the metallocene catalyst and changing the kind andcopolymerization proportion of an α-olefin as a comonomer. The useapplications of the polyolefins obtained by polymerization using themetallocene catalyst have heretofore been mainly developed into fieldsof packaging films, chemical containers, etc. However, their use asmaterials for balloon-tip catheters has not been proposed.

The present inventors have carried out an investigation as to whetherpolyolefins produced using a metallocene catalyst are suitable formaterials for forming a balloon of a balloon-tip catheter for dilationor not. As a result, it has been found that balloons excellent inbalance among various properties such as shapeability, retention ofshape, flexibility and breaking strength compared with low densitypolyethylene (LDPE) and linear low density polyethylene (LLDPE) obtainedby polymerization using the conventional multi-site catalyst such as aZiegler-Natta catalyst can be provided from them.

By the way, changes in physical properties in a forming and processingstep of a balloon and the manner of application of force upon use areextremely complex, and it has also been found that among polyolefinsobtained by polymerization using the metallocene catalyst,ethylene-α-olefin copolymers obtained by polymerization using themetallocene catalyst are preferred in order to provide balloons farexcellent in such various properties as described above, andethylene-α-olefin copolymers having a low melting point and high tensilebreak strength are more preferred. Further, it has been found that whena copolymer having a great difference between the melting point and thesoftening point and a high ratio of the tensile break strength to thetensile yield strength is selected for use, a balloon markedly improvedin such required properties as described above can be provided. Thepresent invention has been led to completion on the basis of thesefindings.

According to the present invention, there is thus provided a balloon-tipcatheter having a balloon formed from a polymeric material in thevicinity of the tip of a catheter, wherein the polymeric materialforming the balloon comprises a polyolefin obtained by polymerizationusing a metallocene catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating an exemplary balloon-tipcatheter for dilation.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, a polymeric material comprising a polyolefinproduced by a polymerization reaction using a metallocene catalyst isused as a material for forming a balloon of a balloon-tip catheter fordilation.

The metallocene catalyst (also referred to as a Kaminsky catalyst orsingle-site catalyst) is composed of a metallocene compound of astructure that a transition metal is held between unsaturated compoundsof a π electron system, and is used in combination with a promotor suchas methylaluminoxane or an organoaluminum compound. As examples of themetallocene compound, may be mentioned those containing one or two(substituted) cyclopentadienyl groups, (substituted) indenyl groups,(substituted) tetrahydroindenyl groups or (substituted) fluorenylgroups, or a group obtained by crosslinking 2 groups of these groups bycovalent bonding bonded to a transition metal of Group IVA, such aszirconium, titanium or hafnium, and having ligands such as hydrogenatoms, oxygen atoms, halogen atoms, alkyl groups, alkoxy group, arylgroups, acetylacetonato groups, carbonyl groups, nitrogen molecules,oxygen molecules, Lewis bases, silicon atom-containing substituents orunsaturated hydrocarbons. As the promotor, there may also be used acompound which is an ionic or electrophilic compound formed from an ionpair of a cation and an anion and becomes a stable ion by reacting witha metallocene compound to form an active species for polymerization, forexample, tetrakis-(pentafluorophenyl)boron.

Examples of a monomer for obtaining the polyolefin by polymerizationinclude ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene,1-heptene, 4-methyl-1-pentene, 4-methyl-1-hexene and4,4-dimethyl-1-pentene. These monomers may be used either singly or inany combination thereof.

The polyolefin is preferably polyethylene or an ethylene-α-olefincopolymer from the viewpoint of various properties of the resultingballoon, with the ethylene-α-olefin copolymer being particularlypreferred. The ethylene-α-olefin copolymer can be obtained bycopolymerization of ethylene and an α-olefin using a metallocenecatalyst. As a comonomer, an α-olefin having 4 to 40 carbon atoms ispreferably used. Examples of the α-olefin include 1-butene, 1-pentene,1-hexene, 1-octene, 1-heptene, 4-methyl-1-pentene, 4-methyl-1-hexene and4,4-dimethyl-1-pentene. Of these, α-olefins having a 4 to 12 carbonatoms are preferred, with α-olefins having 4 to 10 carbon atoms beingparticularly preferred. The copolymerization proportion of the α-olefinis generally 2 to 50 wt. %, preferably 5 to 40 wt. %, more preferably 10to 30 wt. %.

Examples of a (co)polymerization process for obtaining the polyolefin byusing the metallocene catalyst include vapor-phase, solution, bulkpolymerization, high-pressure and slurry processes. The polymerizationis generally conducted under conditions of a polymerization temperatureof −100 to 250° C., polymerization time of 5 minutes to 10 hours and areaction pressure of ordinary pressure to 300 kg/cm².

The melt flow rate (MFR; JIS K 7210) of a polyolefin such as anethylene-α-olefin copolymer obtained by polymerization using themetallocene catalyst is generally 0.1 to 30.0 g/10 min, preferably 1.0to 20.0 g/10 min, more preferably 1.0 to 15.0 g/10 min, most preferably1.5 to 15.0 g/10 min. If MFR is too low, the resulting balloon isdifficult to achieve sufficient strength. If MFR is too high, theforming or molding ability of the polyolefin is deteriorated. Thedensity (JIS K 7112) of the polyolefin is generally 0.950 g/cm³ orlower, preferably 0.850 to 0.940 g/cm³, more preferably 0.880 to 0.930g/cm³. If the density is too low, the resulting balloon tends to causedisadvantages such as blocking due to sticking on the surface thereof.If the density is too high, the transparency of the balloon is lowered.

In the polyolefin obtained by polymerization using the metallocenecatalyst, the molecular weight distribution is narrow because themetallocene catalyst having an even active site is used, and moreoverthe composition distribution also becomes narrow in the case of acopolymer such as an ethylene-α-olefin copolymer because the α-olefin asa comonomer is uniformly introduced into the main ethylene chain.Therefore, a component (sticky portion) having a low molecular weightand a low density becomes little, and a component extracted with anorganic solvent also becomes little. When a polyethylene resin is usedto form a film, spherulites are formed. Units forming the spherulitesinclude a lamella (thin layer like a single crystal). In theethylene-α-olefin copolymer making use of the metallocene catalyst, thelamella is thin, and on the other hand, tie molecules tying lamellae toeach other are present in plenty. These facts permit the formation of atough film.

The polyolefin making use of the metallocene catalyst, such as theethylene-α-olefin copolymer, may be synthesized. However, many kinds ofpolyolefins have been already produced and marketed, and so a marketedproduct may also be used. Since changes in physical properties informing and processing of a balloon using a polymeric material and themanner of application of force upon use of the balloon are extremelycomplex as described above, however, it is desirable to select apolyolefin capable of imparting particularly excellent balloonproperties from among the polyolefins obtained by polymerization usingthe metallocene catalyst. When the polyolefins obtained bypolymerization using the metallocene catalyst are used in variousapplication fields, their densities, the kinds and amount of comonomersused, MFR, etc. are used as indices. When they are used as materials forballoons, however, it is not always proper to use these as indices.

The present inventors have carried out an investigation as to variouspolymeric materials. As a result, it has been found that amongpolyolefins obtained by polymerization using the metallocene catalyst,polyethylene resins such as polyethylene and ethylene-α-olefincopolymers are preferred in order to provide balloons excellent inprocessability and moreover in various properties when formed andprocessed into the balloons, with ethylene-α-olefin copolymers beingparticularly preferred. As a result of a further investigation, it hasalso been found that a polyolefin obtained by polymerization using themetallocene catalyst preferably has a melting point of 125° C. or lowerand tensile break strength of 250 kg/cm² or higher, and more preferablyhas a melting point of 120° C. or lower and tensile break strength of350 kg/cm² or higher. In particular, the use of an ethylene-α-olefincopolymer obtained by polymerization using the metallocene catalyst andhaving a melting point as low as 120° C. or lower and tensile breakstrength as high as 350 kg/cm² or higher is most preferable because aballoon far excellent in flexibility and breaking strength and also goodin shapeability and retention of shape can be provided.

Accordingly, a polyolefin produced using the metallocene catalyst andhaving such specific physical properties, particularly, anethylene-α-olefin copolymer is used as a material for forming a balloon,whereby a balloon high in strength, good in flexibility, capable ofdesigning compliance within a proper range and easy to shape into aballoon and fusion-bond it to a catheter can be provided. Theethylene-α-olefin copolymer contains tie molecules tying lamellae toeach other in plenty in proportion to the low melting point and easyforming and processing into a balloon, so that a balloon having highstrength can be provided.

In the polyolefins such as the ethylene-α-olefin copolymers producedusing the metallocene catalyst, a difference (melting point-softeningpoint) between the melting point and the softening point is preferablyat least 15° C. When a polyolefin great in the difference between themelting point and the softening point and low in softening point isused, the shaping of the resulting balloon is easy when the balloon isfolded, and its setting ability becomes good. The balloon-tip catheterfor dilation is shaped into, for example, a fixed form that a balloon iswound around a catheter in order to facilitate its insertion into andextraction from a coeloma such as a vessel, and the fixed form is oftenretained while the balloon is deflated under reduced pressure. However,low density polyethylene (LDPE), which is the conventional material forballoon, is low in melting point, but relatively high in softening pointand is not always sufficient in shapeability and retention of shape.Linear low density polyethylene (LLDPE) obtained by polymerization usingthe conventional multi-site catalyst is great in a difference betweenthe melting point and the softening point, but high in melting point andalso relatively high in softening point. Therefore, its shapeability andretention of shape are insufficient.

In the polyolefins such as the ethylene-α-olefin copolymers producedusing the metallocene catalyst, a ratio of the tensile break strength(TB) to the tensile yield strength (Tγ) is preferably at least 3.0times. Since the polyolefins such as the ethylene-α-olefin copolymershaving such physical properties have high tensile break strength andmoreover a high ratio of the tensile break strength to the tensile yieldstrength compared with, for example, the conventional polyethyleneresins, they are easy to be stretched upon the forming and processing ofballoons and hence to gain the effect of the stretching. Theethylene-α-olefin copolymers obtained by polymerization using themetallocene catalyst are narrow in molecular weight distribution andexcellent in uniform stretchability. However, with respect to thoseproduced using a process comprising subjecting a tubular parison tostretch blow molding, like a balloon, the stretching tends to becomeuneven due to the thickness irregularity of the tube. However, anethylene-α-olefin copolymer having a ratio of the tensile break strengthto the tensile yield strength of at least 3.0 times is extremely low intensile yield strength compared with the tensile break strength.Therefore, even when a balloon is formed from such a copolymer by, forexample, stretch blow molding, and thickness irregularity is present ina tubular parison, uniform stretching can be performed over the wholeballoon. In addition, since the tensile break strength is high, ahigh-quality and high-strength balloon is provided.

Further, when a polyolefin such as an ethylene-α-olefin copolymer havinga high ratio of the tensile break strength to the tensile yield strengthis used, a balloon having a compliance (rate of change in the diameterof the balloon inflated to the dilation pressure of the balloon) uponinflation of the balloon within a proper range, for example, it beinglow compared with the conventional polyethylene resins, and on the otherhand being high compared with polyester resins and polyamide resins, canbe provided. If the compliance is too high, it is difficult to stablydilate a vessel. If the compliance is too low, it is difficult toefficiently dilate the vessel.

The balloon according to the present invention is excellent inflexibility in spite of high strength due to even molecular weight,small and even thin spherulite layer (lamella) and high presenceprobability of tie molecules tying these lamellae to each other, whichare characteristic of the polyolefin such as the ethylene-α-olefincopolymer obtained using the metallocene catalyst, so that a balloonwhich is not stiff even when it is deflated under reduced pressure canbe provided. On the other hand, the use of a polymeric material of thepolyamide or polyester type, the molecular chain of which is high incrystallinity, results in a stiff balloon.

In the present invention, the polymeric material forming the ballooncomprises a polyolefin obtained by polymerization using the metallocenecatalyst, particularly preferably, an ethylene-α-olefin copolymer havingthe following features:

(1) the melting point being 120° C. or lower;

(2) the tensile break strength being at least 350 kg/cm²;

(3) a difference between the melting point and the softening point beingat least 15° C.; and

(4) a ratio (TB/Tγ) of the tensile break strength (TB) to the tensileyield strength (Tγ) being at least 3.0.

The melting point of the ethylene-α-olefin copolymer is preferablywithin a range of 95 to 120° C., more preferably 100 to 120° C. Thesoftening point thereof is preferably within a range of 70 to 105° C.,more preferably 75 to 103° C. The difference between the melting pointand the softening point is preferably within a range of 15 to 50° C.,more preferably 15 to 45° C. The tensile break strength is preferablywithin a range of 350 to 500 kg/cm², more preferably 355 to 450 kg/cm².The ratio (TB/Tγ) of the tensile break strength (TB) to the tensileyield strength (Tγ) is preferably within a range of 3.0 to 10.0, morepreferably 3.5 to 8.0.

In the present invention, the polyolefin obtained by polymerizationusing the metallocene catalyst, particularly preferably, theabove-described specific ethylene-α-olefin copolymer may be used byitself as the polymeric material for forming the balloon. However,various kinds of additives, and other resins and elastomers may beincorporated so far as no detrimental influence is thereby imposed onthe object of the present invention.

As the additives, several of, for example, antioxidants, ultravioletabsorbents, antistatic agents, flame retardants, metal deactivators,pigments, dyes, nucleating agents, etc. may be added as needed. In thiscase, the amount added is generally 20 parts by weight or less,preferably 5 parts by weight or less per 100 parts by weight of thepolyolefin though it varies according to the required properties of theresulting balloon.

Examples of other resins include various resins obtained bypolymerization using a Ziegler-Natta catalyst, for example, polyolefinresins such as polypropylene resins, high density polyethylene, linearlow density polyethylene, ultra low density polyethylene,high-pressure-processed low density polyethylene, ethylene-vinyl acetatecopolymers, ethylene-acrylic ester copolymers, ethylene-acrylic acidcopolymers, ethylene-methacrylic acid copolymers and ethylene-carbonmonoxide copolymers; and various kinds of thermoplastic resins such asamorphous polystyrene resins, crystalline polystyrene resins, polyvinylchloride resins, polyamide, polyacetal and polycarbonate. The blendingproportion of these other resins is generally 100 parts by weight orlower, preferably 50 parts by weight or lower, more preferably 30 partsby weight or lower per 100 parts by weight of the polyolefin.

As the elastomers, there may be used, for example, solid rubbers such asethylene-propylene rubber, ethylene-1-butene rubber, propylene-l-butenerubber, styrene-butadiene rubber and hydrogenated products thereof,isoprene rubber, neoprene rubber, and acrylonitrile-butadiene rubber andhydrogenated products thereof; styrene type thermoplastic elastomerssuch as styrene-butadiene block copolymer elastomers and hydrogenatedproducts thereof; and other various elastomers. The blending proportionof the elastomers is generally 100 parts by weight or lower, preferably50 parts by weight or lower, more preferably 30 parts by weight or lowerper 100 parts by weight of the polyolefin.

In the present invention, mixing of other components into the polyolefinis conducted by liquid mixing or solid mixing. However, melt mixing aregenerally used. For example, any of various kneaders such as rolls,screw mixers, Banbury mixer, kneaders, blenders and mills is used toknead the respective components at a desired temperature, and thekneaded mixture is then pelletized into particles of a proper size. Inthis case, any process of strand cut process, underwater cut process,hot cut process, mist cut process, sheet cut process, freeze grindingprocess and melt spraying process may be used.

As a process for forming a balloon from the polymeric materialcomprising the polyolefin, a process comprising preparing a tubularparison in accordance with a method known per se in the art andsubjecting the tubular parison to stretch blow molding in a mold isadopted. An extrusion process, a copper wire coating process or the likeis adopted for the formation of the tubular parison. The temperature ofthe blow molding is generally about 30 to 180° C., preferably about 80to 120° C. The draw ratio in a machine direction is preferablycontrolled to at least 130%, and the effective total draw ratio(sectional area of tube/sectional area of balloon) is preferablycontrolled to at least 5 times. After stretch blow molding, a heattreatment may be conducted to prevent the resulting balloon from causinggreat heat shrinkage by subsequent heat history.

The tubular parison may be subjected to stretch blow molding as it is,or if desired, after crosslinking it by irradiation of ionizingradiation such as electron beams. The pressure resistance of the ballooncan be improved by the radiation crosslinking. The irradiation dose isgenerally about 2 to 15 MR. The gel fraction of the tube crosslinked bythe irradiation is preferably controlled to generally about 0.75 to0.95. The gel fraction can be determined as insoluble matter in heatedxylene contained in a crosslinked sample. More specifically, 0.1 g ofthe crosslinked sample is heated for 6 hours in 100 ml of xylene heatedto 120° C., soluble matter is then separated by filtration, and the dryweight of the remaining crosslinked sample is measured to calculate outits proportion to the crosslinked sample before the treatment.

The balloon thus obtained may be used as it is, and another layer suchas a polyurethane coating may be laminated thereon if desired. Besides,the surface of the balloon may also be coated with any of various kindsof natural or synthetic hydrophilic polymers to enhance the lubricity ofthe balloon in blood or a physiological saline.

In the present invention, the polymeric material comprising thepolyolefin obtained by polymerization using the metallocene catalyst,preferably, the specific ethylene-α-olefin copolymer is used as amaterial for forming a balloon. Therefore, a thin balloon excellent inprocessability into a balloon and high in strength can be provided. Thisballoon is good in shapeability, retention of shape, flexibility and thelike, and its compliance also falls within a proper range. The balloonis also excellent in fusion-bonding ability to a catheter. Accordingly,the use of this balloon permits the provision of a balloon-tip catheterfor dilation satisfying the highly required properties. The size of theballoon may be suitably determined according to a site applied. In thecase of a balloon-tip catheter for vasodilation, however, the length isabout 10 to 100 mm, and the outer diameter is about 2 to 10 mm. The filmthickness of the balloon is generally about 5 to 100 μm, preferablyabout 10 to 50 μm. When the catheter is applied to a peripheral coronaryartery, however, the balloon may be made low profile.

The balloon-tip catheters according to the present invention have aballoon formed from the polymeric material comprising the polyolefinobtained by polymerization using the metallocene catalyst in thevicinity of the tip of a catheter. A typical example thereof illustratesin FIG. 1. As examples of the material of the catheter, may be mentionedgeneral-purpose polymeric materials such as high density polyethylene,polyvinyl fluoride and polyimide. However, the same polyolefin obtainedby polymerization using the metallocene catalyst as that used in theballoon may be used.

EXAMPLES

The present invention will hereinafter be described more specifically bythe following Examples and Comparative Examples.

Examples 1 to 6 and Comparative Examples 1 to 4

(1) Forming and Processing of Balloon:

Respective resins having their corresponding material characteristicsshown in Tables 1 and 2 were used as materials for forming balloons toproduce raw tubes each having an outer diameter of about 1 mm and a wallthickness of 50 μm by extrusion. Each of the raw tubes was cut intolengths of 100 mm to prepare a tubular parison. The tubular parison wasplaced in an outer mold for balloon having an inner diameter 4 mm and alength of 30 mm to conduct blow molding under conditions that a moldingtemperature is preset within a range from 0.5 to 0.8 times of themelting point of each resin, and a molding pressure within 8±4 kg/cm²,and the blown parison was stretched in a radial direction, therebyforming and processing a balloon.

(2) Fusion Bonding of Balloon:

Each balloon formed and processed above was fusion-bonded to a cathetertube (made of polyethylene) having an outer diameter of 1 mm and a wallthickness of 200 μm. The fusion-bonding temperature was controlled to(the melting point of each resin ±0.2° C.).

(3) Shaping of Balloon:

Each balloon-tip catheter produced above was placed under reducedpressure to wind the balloon in the circumferential direction of thecatheter, and the balloon-tip catheter was then covered with a sheathfor retaining the shape to conduct shaping at 70° C. for 1 hour.

(4) Evaluation of Properties:

After the shaping step, the balloon-tip catheter was taken out of thesheath to evaluate its properties. (n=30)

{circle around (1)} Shapeability:

After the sheath was removed, the form of the balloon under reducedpressure was observed to evaluate the shapeability in accordance withthe following standard:

◯: The balloon was completely wound around the catheter;

Δ: The winding form of the balloon was somewhat disordered; and

X: The winding form of the balloon was disordered.

{circle around (2)} Retention of shape:

The balloon was inflated and deflated again under reduced pressure toobserve the form of the balloon, thereby evaluating the retention ofshape in accordance with the following standard:

◯: The balloon was completely wound around the catheter;

Δ: The winding form of the balloon was somewhat disordered; and

X: The winding form of the balloon was disordered.

{circle around (3)} flexibility:

After the sheath was removed, the balloon under reduced pressure washeld between fingers to evaluate the flexibility from its hardness inaccordance with the following standard:

◯: Felt flexible and soft;

Δ: Felt somewhat hard; and

X: Felt hard and stiff.

{circle around (4)} Breaking strength:

An internal pressure was applied to balloons to measure a pressure underwhich at least 90% of the balloons were not broken.

TABLE 1 Example 1 2 3 4 5 6 Metallocene-catalyzed ethylene-α- olefincopolymer Material for balloon A B C D E F Material Characteristics:Tensile break strength T_(B) 400 400 360 360 350 270 [kg/cm²] Tensileyield strength T_(γ) 57 56 105 100 140 60 [kg/cm²] T_(B)/T_(γ) 7.0 7.13.4 3.6 2.5 4.5 Melting point [° C.] 113 103 117 113 121 108 Softeningpoint [° C.] 79 81 101 98 110 75 (Melting point - Softening 34 22 16 1511 33 point) [° C.] Hardness 45 45 55 54 56 43 Forming and processing ofballoon: Molding temperature [° C.] 80 73 83 80 88 77 Molding pressure[kg/cm] 6.7 6.1 7.0 6.7 7.2 6.5 Fusion-bonding temperature 112 102 115112 122 109 [° C.] Shaping temperature [° C.] 70 70 70 70 70 70 Balloonsize: Outer diameter [mm] 4.0 4.0 4.0 4.0 4.0 4.0 Filmn thickness [μm]24 24 24 24 24 24 Length [mm] 30 30 30 30 30 30 Evaluation of balloon:Shapeability ◯ ◯ ◯ ◯ Δ Δ Retention of shape ◯ ◯ ◯ ◯ Δ Δ Flexibility ◯ ◯◯ ◯ Δ Δ Break strength [kg/cm²] 20 20 18 18 10 10

TABLE 2 Comparative Example 1 2 3 4 LLDPE Material for balloon {circlearound (1)} {circle around (2)} {circle around (3)} LDPE Materialcharacteristics: Tensile break strength T_(B) [kg/cm²] 390 390 300 215Tensile yield strength T_(γ) [kg/cm²] 140 130 110 105 T_(B)/T_(γ) 2.73.0 2.7 2.0 Melting point [° C.] 127 127 124 111 Softening point [° C.]108 105 102 98 (Melting point - Softening point) [° C.] 19 22 22 13Hardness 61 56 55 51 Forming and processing of balloon: Moldingtemperature [° C.] 80 90 88 79 Molding pressure [kg/cm] 7.6 7.6 7.4 6.6Fusion-bonding temperature [° C.] 129 129 125 113 Shaping temperature [°C.] 70 70 70 70 Balloon size: Outer diameter [mm] 4.0 4.0 4.0 4.0 Filmthickness [μm] 24 24 24 24 Length [mm] 30 30 30 30 Evaluation ofballoon: Shapeability Δ Δ Δ Δ Retention of shape X X X Δ Flexibility X XΔ Δ Break strength [kg/cm²] 10 9 9 6

Measuring Method

Tensile Break Strength and Tensile Yield Strength

A test was made by means of an Instron type tensile tester in accordancewith JIS K 7127-1989. The tensile break strength means tensile stress atbreak of a specimen, and the tensile yield strength means stresscorresponding to the first point at which increase in elongation isobserved without increase in load on a load-elongation curve.

Resins Used:

(1) Resin A: an ethylene-1-hexene copolymer (density=0.905 g/cm³,MFR=2.2 g/10 min),

(2) Resin B: an ethylene-1-hexene copolymer (density=0.910 g/cm³,MFR=3.5 g/10 min),

(3) Resin C: an ethylene-1-hexene copolymer (density=0.917 g/cm³,MFR=2.0 g/10 min),

(4) Resin D: an ethylene-1-hexene copolymer (density=0.915 g/cm³,MFR=4.0 g/10 min),

(5) Resin E: an ethylene-1-hexene copolymer (density=0.928 g/cm³,MFR=2.0 g/10 min),

(6) Resin F: an ethylene-1-hexene copolymer (density=0.905 g/cm³,MFR=11.0 g/10 min),

(7) LLDPE {circle around (1)}: (density=0.926 g/cm³, MFR=0.8 g/10 min),

(8) LLDPE {circle around (2)}: (density=0.926 g/cm³, MFR=0.3 g/10 min),

(9) LLDPE {circle around (3)}: (density=0.924 g/cm³, MFR=0.3 g/10 min),

(10) LDPE: (density=0.923 g/cm³, MFR=0.25 g/10 min).

As apparent from the results shown in Tables 1 and 2, the balloon-tipcatheters according to the present invention are good in balloonproperties. In particular, the balloons formed with an ethylene-α-olefincopolymer obtained by polymerization using the metallocene catalyst andhaving a melting point of 120° C. or lower, tensile break strength of350 kg/cm² or higher, a difference between the melting point and thesoftening point of at least 15° C and a ratio of the tensile breakstrength to the tensile yield strength of at least 3.0 times were suchthat the shapeability, retention of shape, flexibility and breakingstrength are markedly excellent, their compliance falls within a properrange, and a vessel can be safely and efficiently dilated. Accordingly,the balloon-tip catheters according to the present invention areparticularly suitable for use as balloon-tip catheters for dilation.

INDUSTRIAL APPLICABILITY

According to the present invention, there are provided balloon-tipcatheters having a balloon which is high in strength, excellent inflexibility, easy to shape the balloon when it is folded, good insetting ability, has a compliance within a proper range when it isinflated, and moreover is excellent in processability, retention ofshape and fusion-bonding ability to a catheter, and being suitable foruse as balloon-tip catheters for dilation.

What is claimed is:
 1. A balloon-tip catheter having a balloon formedfrom a polymeric material in the vicinity of the tip of a catheter,wherein the polymeric material forming the balloon comprises anethylene-α-olefin copolymer obtained by polymerization using ametallocene catalyst.
 2. The balloon-tip catheter according to claim 1,wherein the ethylene-α-olefin copolymer is a copolymer of ethylene andan α-olefin having 4 to 40 carbon atoms.
 3. The balloon-tip catheteraccording to claim 2, wherein the ethylenie-α-olefin copolymer has amelting point of 125° or lower and tensile break strength of 250 kg/cm²or higher.
 4. The balloon-tip catheter according to claim 2, wherein theethylene-α-olefin copolymer has a melting point higher by at least 15°C. than the softening point thereof.
 5. The balloon-tip catheteraccording to claim 2, wherein the ethylenc-α-olefin copolymer has aratio of the tensile break strength to the tensile yield strength of atleast 3.0 times.
 6. The balloon-tip catheter according to claim 2,wherein the ethylene-α-olefin copolymer is a copolymer of ethylene andan α-olefin having 4 to 12 carbon atoms.
 7. The balloon-tip catheteraccording to claim 1, wherein the ethylene-α-olefin copolymer has amelting point of 125° C. or lower and tensile break strength of 250kg/cm² or higher.
 8. The balloon-tip catheter according to claim 7,wherein the ethylene-α-olefin copolymer has a melting point of 120° C.or lower and tensile break strength of 350 kg/cm² or higher.
 9. Theballoon-tip catheter according to claim 1, wherein the ethvlene-α-olefincopolymer has a melting point higher by at least 15° than the softeningpoint thereof.
 10. The balloon-tip catheter according to claim 1,wherein the ethylene-α-olefin copolymer has a ratio of the tensile breakstrength to the tensile yield strength of at least 3.0 times.
 11. Theballoon-tip catheter according to claim 1, wherein the ethylene-α-olefincopolymer is an ethylene-u-olefin copolymer having the followingfeatures: (1) the melting point being 120° C. or lower; (2) the tensilebreak strength being at least 350 kg/cm²; (3) a difference between themelting point and the softening point being at least 15° C.; and (4) aratio (TB/Tγ) of the tensile break strength (TB) to the tensile yieldstrength (Tγ) being at least 3.0.
 12. The balloon-tip catheter accordingto claim 1, which is a balloon-tip catheter for dilation.